Not so long ago Roentgen-ray crystallography was a rather esoteric science reserved for a fairly small group of specialists. Perusal of the recent literature shows that the number of publications per year con cerned with crystal structure analysis by x-ray diffraction has increased by a factor of ten in the last ten years. This great increase can be at tributed to a number of factors. An analysis of a molecule which may contain eighty atoms, excluding hydrogen atoms, involves the collection of about 6000 independent reflections. Before the advent of the automatic diffractometer, an instrument...